A tubular implant structure which is within a radial range and within an axial range expandable and contractable is well known in the field of intraluminally deliverable implants. A so-called “stent” is a well-known example of such a structure. Such a structure is usually introduced into the body of a human or an animal and delivered to a site within that body where the tubularity of the structure can play a crucial role in the functioning of at least that part of the body. That part is usually a part of the vascular system of the body, but can also be a part of another system of the body, for instance the biliary system or the digestive system.
A catheter is often used for delivery at the implant site. Whilst being delivered, the diameter of the tubular implant structure is preferably as small as possible. Currently, the diameter can be as small as 6-5 French (three French being equal to 1 mm). Once arrived at the implant site, the tubular implant structure is usually made to expand so that its diameter reaches a diameter within a predetermined range, for instance 18-24 F. Given these transformations, it will be appreciated that the tubular implant structure is often a complex device comprising struts connected in a sophisticate manner so that the structure can do the required “job”.
Referring again to the example of a stent, in the radially expanded condition, it provides a “scaffolding” that internally supports the inner wall of a lumen and helps keeping the lumen open so that the fluid flow through that lumen can continue. For the vascular system is the lumen part of a vessel and the fluid flow a blood flow.
As usually the part of the body in which the tubular implant structure has been implanted, may be subjected to various types of movement, it is necessary to know in advance the behaviour of the implant structure when subjected to such movements and its behaviour after having been subjected to a number of such movements that may occur during the remaining lifetime of the body. In particular structures implanted in ligaments and in for instance the neck, may experience subjection to various movements, and consequently to deformations such as torsion, axial compression, axial elongation, bending, and combinations thereof.
US 2004/0016301 A1 describes a vascular prosthesis tester that is configured to subject a stent, possibly provided with a graft, to tensile and/or compressive axial loads, bending stresses, and torsional stresses. Actuators may induce the stresses independently or in combination, or in a manner to simulate physiological movement, such as walking. The test member, i.e. the stent or stent-graft, may be disposed upon the outer surface of a fluid conduit. It is also possible that the stent graph is contained within a channel of a fluid conduit. The stent graft is “friction-fit” placed within or around the conduit. A fluid is injected into the central lumen of the conduit to subject the test member to stress as applied by a change of blood pressure in a vessel during the pumping of the heart. The combination of a “friction-fit” connection and possible radial expansion of the test member due to inner radial pressure allows for axial sliding of the test member and thus to ill-defined movement of the test member during the test. In other words, the movement which the test member experiences, is dependent on the way the test member manages to position itself during the test. Furthermore, test members may have been designed differently. The positioning, and consequently the “loading” and deformation of the test member, may be dependent on the design of the test member itself. Different designs might then be subjected to different tests, even though the tests themselves are designed to be equal. This may result in an over-optimistic assessment of the behaviour of test members.
U.S. Pat. No. 5,670,708 describes a high-frequency intravascular prosthesis fatigue tester. The prosthesis such as a stent, a graft and a stent-graft, is subjected to physiologic loading conditions. The prosthesis is positioned within a fluid conduit into which fluids are forced from both ends in a pulsating fashion and at high-frequency, thereby simulating systolic and diastolic pressures. Also in this case, a “friction-fit” retains the prosthesis within the fluid conduit. Consequently, the disadvantage of the earlier described prior art tester equally applies to the tester described in U.S. Pat. No. 5,670,708.
US 2003/0110830 A1 describes a method and apparatus for measuring the compliance of stents and stent-grafts. A stent or stent-graft is positioned within a tissue tube, for instance, a pretested tube, and fixed therein by simply releasing the stent to expand on its own, or by internally expanding a plastically deforming stent using a balloon catheter. The stent or stent graft is oversized with respect to the host lumen to facilitate “anchoring” therein. The testing involves pressurizing the fluid in the lumen of the tubes and at a pulse rate controlling the expansion of the stent or stent graft within the tube to that which would be experienced in vivo. The earlier described disadvantages of the other prior art testers still apply.
It is an object of one embodiment of the invention to provide a fatigue test system for repetitively deforming a substantially tubular implant structure wherein the implant structure is subjected to a well defined predetermined deformation.
It is an object of one embodiment of the invention to provide a fatigue test system that allows for a high reproducibility of tests.
It is an object of one embodiment of the invention to provide a fatigue test system that allows for subjecting the implant structure to a well defined and predetermined deformation, independent of the type of structure.
It is an object of one embodiment of the invention to connect a tubular implant structure to a fatigue test system so that the connection itself is unlikely to contribute to the damage the tubular implant structure experiences during fatigue testing.